1. Field of the Invention
This invention relates to a preform for a large container which is used for a large container made of a polyethylene terephthalate (hereinafter referred to as PET) resin and having a volume of 10 liters or more; the large container; and a method for producing the large container.
2. Description of the Related Art
Large containers made of a resin with a volume of, say, 5 gallons (about 20 liters) have so far been adopted worldwide, for example, as refillable bottles for mineral water. A polycarbonate resin is generally used as a material for such large containers.
Large containers, such as refillable bottles for mineral water, are usually recovered from consumers after their use. They are washed with a cleaning fluid at a temperature of the order of 65° C. (hot water washing), and reused a plurality of times. Thus, a polycarbonate resin excellent in heat resistance has been used preferably as a material for large containers.
In recent years, it has been confirmed that endocrine disrupting chemicals (EDCs) elute from containers made of polycarbonate resins. This has been perceived as a problem all over the world, and there has been a desire for the use of a resin material, which is unlikely to cause the elution of EDC, as a material for the above-mentioned large containers. For example, a PET resin used as a material for small containers for beverages poses no problem of EDC. Thus, the use of the PET resin as a material for large containers is under consideration.
However, a container made of the PET resin generally has low resistance to heat, thus posing the problem that the container deforms (shrinks) during washing with hot water as mentioned above. Under these circumstances, PET resin has not found wide use as a material for a large container which is used as a refillable bottle or the like for mineral water.
To solve the foregoing problems, the applicant of the present application, for example, has proposed a method for biaxially stretching an injection-molded preform by blow molding to produce a large container made of a PET resin, wherein the molded product is annealed at a higher temperature than the temperature of a cleaning fluid (see, for example, Patent Document 1).
With such a method, the heat resistance of the large container made of the PET resin is enhanced, whereby deformation of the large container during hot water washing can be suppressed. However, a further improvement in the heat resistance of the large container has been desired.
With a small container for a beverage, for example, there has been a proposal for a method for producing a container, which comprises primarily blow molding a preform to form a primary blow molded product larger than a final molded product, heat-treating the primary blow molded product to shrink it, and then secondarily blow molding the shrunken product to prepare the final molded product (see, for example, Patent Document 2).